This invention is generally directed towards a method of operating a heat pump water heating system and specifically to a method of detecting and diagnosing operating conditions of a heat pump water heating system.
Chlorine containing refrigerants have been phased out due to environmental considerations. Many alternatives have been proposed for replacing chlorine containing refrigerants including carbon dioxide. Carbon dioxide has a low critical point, which causes most air conditioning systems utilizing carbon dioxide to run partially above a critical point or to run trans-critical under most conditions. The pressure of any sub critical fluid is a function of temperature under saturated conditions (both liquid and vapor present). However, when temperature of the fluid is higher than the critical temperature, the pressure becomes a function of fluid density.
Trans-critical refrigeration systems utilize a refrigerant compressed to high pressure and high temperature in a compressor. As the refrigerant enters a gas cooler, heat is removed from the refrigerant and transferred to a fluid medium such as water. In a heat pump water heater, water heated in the gas cooler is used to heat water within a hot water tank. Refrigerant flows from the gas cooler to an expansion valve. The expansion valve regulates the flow of refrigerant between high-pressure and low-pressure. Control of refrigerant through the expansion valve controls the flow and efficiency of the refrigerant circuit. Refrigerant flows from the expansion valve to an evaporator.
In the evaporator, low-pressure refrigerant accepts heat from the air to become superheated. Superheated refrigerant from the evaporator flows into the compressor to repeat the cycle.
The system is controlled to vary refrigerant and water flow depending on current operating conditions. Degradation of system devices can detrimentally affect system performance and operating costs. Further, in some instances changes in system performance are not readily apparent and can therefore go undetected. Operating costs are greatly reduced by operating the system at optimal conditions. Further, reducing system down time greatly reduces operating costs.
Accordingly, it is desirable to develop a method of detecting system faults and diagnosing system problems to reduce system down time and increase operating efficiency.